Purification of tetrahydrophthalimides with alkaline earth metal hydroxides



Patented Oct. 7, 1952 MIDES WITH ALKALINE EARTH METAL HYDROXIDES Allen R. Kittleson, .Cranford, N. J assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application September 10, 1951,

I Serial No. 245,979

4 Claims. (or. 260-326) This invention relates to a process for the purification of tetrahydrophthalimides and more particularly to the purification of tetrahydrophthalimides for their use in the preparation of N-thiotrichlorornethyl tetrahydrophthalimides.

N-thiotrichloromethyl (or N-trichloromethylthio) tetrahydrophthalimides are disclosed in U. S. Patent No. 2,553,770 as extremely effective parasiticides and especially effective fungicides.

maleic anhydride can be dissolved in a solvent such as benzene and the butadiene bubbled into it. This is done in a stirred reactor with a cooling jacket and the use of excess butadiene. The tetrahydrophthalic anhydride is isolated and dissolved in ammonium hydroxide to form the ammonium salt of the acid amide'which after driving off the excess water and heating, yields the imide.

These compounds are prepared by dissolving 10 Imides prepared in these manners are of satisthe desired imide, in an aqueous alkaline solufactory purity for most purposes. However, the tion, followed by addition of about an equal nature of the impurities present is such as to be molecular quantity of perchloromethyl merparticularly and specifically detrimental in the captan. The mixture is stirred rapidly, concondensation reaction'between sodium tetrahyveniently, until the aqueous medium becomes drophthalimide and perchloromethyl mercaptan acid to litmus, then filtered to obtain the product to give N-trichlor'omethylthio tetrahydrophthalwhich can be air dried. The reactionmay be imide. The mechanism by which these impuricarried out at room temperature. In caseswhere ties act is not known. However, their presence the imide is readily hydrolyzed in alkaline soluresults in (a) slow rate of reaction between tion, it may be advantageous to cool the reaction sodium imide and perchloromethylmercaptan, mixture as low as 0 C. H (b) low yields of N-trichloromethylthiotetrahy- N-thiotrichloromethyl tetrahydrophthalimide, drophthalimide, (c) an imide-mercaptan reaction which is illustrated by Formula I below mixture difiicult to filter and purify.

H2 w The impurity may be removed by distillation l of the crude imide; however, this procedure is C H O frequently not feasible on a large scale due to the \l high temperatures and vacuum required. The EC impurity is similar to the imide with respect to b I NSOCI3 water insolubility, therefore, a simple water He Washing is not effective.

Al The low yields obtained are apparently due to C a positive poisoning efiect of these impurities A rather than the mere decrease in concentration of the active reactants. This positive poisoning Fumula I effect has been established by experiments whereemploys tetrahydrophthalimide as the starting in some of this impurity was deliberately added materiaL to the indicated reaction system and significant Crude tetrahydrophthalimide may be prepared decreases in Yields thereby Obtained.- by a number f means. o of the better ways The present invention is an improved method is by reaction between maleic anhydride and 48 the purification of tetrahydmphthalimides butadiene The buta diene vapors are passed 1S t0 OVBICOIHG the beforecountercurrently upwardly through downflowing mentioned dimculties- The method F P molten maleic anhydride yielding tetrahYdroaddingan alkaline earthmetal hydroxide to the phthalic anhydride. The latter in the molten crude lmlde dlssolved in hot water at a tate is then passed downwardly countercur... temperature Of about to D C- results rently to upwardly rising ammonia vapors, Th in the precipitation of the insoluble alkaline product is then heated to maintain the residue earth fi of the impurlty impurities- The in the molten state and to drive oil ammonia and impullties a then Separated (ml the hot water so as to yield the desired tetrahydrophthaltion, Preferably by filtration The imide than imides. The molten tetrahydrophthalimide is 50 separat out of th aqueous fil r y olin thus obtained by whichever process is utilized for the latter $0 a p ature of about 15 to 30 C. its preparation and has a m31ting point of The imide in the filtrate need. not be isolated t 13 C for subsequent reactions to form N-trichloro- There are several possible variations in the y y pht alim de. preparation of tetrahydrophthalimides. Thus 55 The calcium, barium and strontium hydroxides the amount of hydroxide is possible because ofv the fact that it has been learned that the impurities are acidic in character. Thus a slurry of purified imide in water has a pH, of 7 to 7.5, whereas the crude imide in a'water slurry has a pH of about 3 to i. It is thus possible to determine the mol per cent impurity by titratlng a crude imide sample up to a pH of about 7.5. The calcium hydroxide is then added in approximately the same molar quantity as the impurity present (see Example I below).

It is possible to remove the impurities by treating a dispersion of the crude imide in water with a sufiicient quantity of sodium hydroxide or any other alkali metal hydroxide which will form a water-soluble salt of the impurity to increase the pH of the slurry to 7.5. The mixture is then filtered and the residual purified imide washed with a small quantity or" water. This method, though effective, results in loss of imide dissolved in the water (solubility=2-2.5% at 25 C.) vAlso it is necessary to isolate the imide from the water slurry, which involves considerable handling on a large scale. This method is therefore not as desirable as the alkaline earth metal hydroxide process detailed above.

The improved method of this invention is illustrated by the following example:

Example I A sample g.) of crude tetrahydrophthalimide Was dispersed in water at room temperature and the pH of the aqueous slurry found to be 3.8. Standard NaOI-I Was added to the slurry until the pH had increased to 8.5; this required 40.5 cc. of 0.1408 N NaOH. This indicates that the crude imide contains 5.7 mol per cent of material titrating below a pH of 8.5 (assuming one acidic group per molecule). This titration was then used as a basis for estimating the quantity of lime to be added in the imide purification A crude imide was converted to the alkali metal salt, which was then reacted with perchloromethyl rnercaptan so as to prepare compound N- trichloromethylthiotetrahydrophthalimide. The time required for the completion of the reaction,

for the filtration and the yield was determined.

Another sample of crude imide was treated with calcium hydroxide as taught in this invention and Example I. After this latter treatment the imide was reacted to form N-trichloromethylthiotetrahydrophthalimide in exactly the same manner as the crude imide not subjected to the treatment of this invention. The results are listed below:

N-trlchloro- Time Bemethylthiotetra- C quirledzfor f hydrophthalimide omp e ion 0 Na Imide 0180013 Time Ro- Reaction quired for Yield Filtration Minutes Minutzs Percent Crude 70 78 Crude-tree ted with Ca(OH); 31 10 57. 6

The improvement in time of reaction, time required for filtration and yield is so clear cut as to require no comment.

The process of this invention is applicable to the purification of other tetrahydrophthalimides such as endomethylene tetrahydrophthalimide, and other products obtained from condensation of a diene and maleic anhydride followed by condensation with ammonia (for example, the imide of the adduct of isoprene with maleic anhydride).

It is apparent that the indicated separations obtained by filtration ca also be accomplished by a wide Variety of other filtering, settling and decanting means.

It is to be understood that the invention is not limited to the specific examples, which have been offered merely as illustrations, and that modifications may be made without departing from the spirit of this invention.

What is claimed is:

1. A process for the purification of a tetrahydrophthalimide which comprises the steps of dissolving the crude imide in water maintained at a temperature in the range of about to 0., adding an alkaline earth metal hydroxide to the resulting solution maintained in the same temperature range so as to precipitate water-insoluble impurities therefrom, and separating the impurities while hot fromthe residual solution so as to leave a purified tetrahydrophthalimide solution.

2. A process as in claim 1 in which the alkaline earth metal hydroxide is added in an amount about equivalent to the mol per cent impurity in the crude imide as determined by titrating a solution of the latter up to a pH in the range of about 7.0-7.5.

3. A process as in claim 2 in which the alkaline earth metal hydroxide is calcium hydroxide.

4. A process for the purification of tetrahydrophthalimide which comprises the steps of dissolving crude tetrahydrophthalimide in water maintained at a temperature in the range of 75 to 100 C.; adding to this solution maintained at approximately the same temperature calcium hydroxide in an equivalent amount to the mol per cent impurity in the crude imide as determined by titrating a crude imide sample up to a pH of about 7.5, so as to precipitate waterinsoluble calcium salt impurities; filterin the resulting system maintained at approximately the same temperature as in the preceding step so as to remove'the Water-i1isoluble calcium salts of the impurities therefrom; and cooling the residual aqueous filtrate to approximately 15 to 30 C. to crystallize the purified tetrahydrophthalimide out of solution.

ALLEN R. KI'ITLESON.

No references cited. 

1. A PROCESS FOR THE PURIFICATION OF A TETRAHYDROPHTHALIMIDE WHICH COMPRISES THE STEPS OF DISSOLVING THE CRUDE IMIDE IN WATER MAINTAINED AT A TEMPERATURE IN THE RANGE OF ABOUT 75* TO 100* C., ADDING AN ALKALINE EARTH METAL HYDROXIDE TO THE RESULTING SOLUTION MAINTAINED IN THE SAME TEMPERATURE RANGE SO AS TO PRECIPITATE WATER-INSOLUBLE IMPURITIES THEREFROM, AND SEPARATING THE IMPURITIES WHILE HOT FROM THE RESIDUAL SOLUTION SO AS TO LEAVE A PURIFIED TETRAHYDROPHTHALIMIDE SOLUTION. 